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ABOUT THIS IMAGE:

These postage-stamp-size images reveal 36 young galaxies caught in the
act of merging with other galaxies. These galaxies appear as they
existed many billions of years ago. Astronomers have dubbed them
"tadpole galaxies" because of their distinct knot-and-tail shapes, which
suggest that they are engaging in galactic mergers.

The galaxies were captured in 2004 in the Hubble Space Telescope's Ultra
Deep Field (HUDF) survey of thousands of distant galaxies. They are part
of more than 165 tadpole galaxies in the HUDF studied recently by a team
of astronomers. The team was looking for indications of black hole
activity in these young galaxies. A characteristic signature of such
activity is a fluctuation in brightness over time, an indication that a
black hole is feasting on surrounding stars and gas. The flickering
light does not come from the black hole itself but from the area
immediately surrounding the black hole. Astronomers did not see
brightness fluctuations in any of the tadpole galaxies they surveyed.
They did, however, observe the fluctuations in 46 different faint galaxies
in the HUDF. These galaxies existed millions of years after the tadpole
galaxies. This result suggests that black holes did not begin eating
when galaxies merged. Rather, it took several hundred million years
for the gas and stars from the merger to arrive on the black hole's
dinner plate and become visible as flickering light. This finding agrees
with recent computer models which predicted that the feeding habits of
black holes would become visible after galactic mergers.

Each postage-stamp image is roughly 84,000 light-years on a side, which
is about the size of our Milky Way Galaxy today. The tadpole galaxies
are shown in the middle of each image and are considerably smaller than
today's giant galaxies. The image was taken by Hubble's Advanced Camera
for Surveys.